Many devices have been used and proposed for recording body movements, and breathing movements. One example is ECG measurements which require the application of ECG electrodes to a patients skin are able to provide “one off” diagnostic information, as well as being used over a period of time for patient monitoring.
U.S. Pat. No. 5,989,193 (the entire contents of which are incorporated herein by reference) by the same inventor as the subject invention, discloses a device and method for detecting and recording the snoring of a patient. This device relies on pressure detectors or accelerometers, placed on or under the patient's mattress. The pressure detector is typically a piezoelectric transducer and the accelerometer may comprise an integrated circuit containing a floating piezoelectric transducer.
International Patent Application No PCT/AU01/00732 also by the same inventor, discloses a biophysical sensor which includes a PVDF (polyvinilidene fluoride) sound vibration sensing element and two or more signal processing paths for producing output signals. Output signals may be two or more of heart sounds, heart movement breathing movement and breath sounds.
However the problem with existing sensors is that they can be intrusive and have to be attached or pressed directly against a patient's chest wall or the like—as in the case of stethoscopes and ECG devices. In the case of those sensors built into e.g. mattresses which a patient lies on, these do not always reliably pick up sounds such as breath sounds. This is due in part to the number of layers of material that the sensor must detect sound through such as the patient's clothing, bed sheets, mattress cover etc. Also the sensors may make the mattress uncomfortable and disturb the patient's sleep.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.